Manufacture of artificial filamentary materials of high bulk



NTARY MATERIALS OF HIGH BULK Aug. 18, 1959 J. w. GREBBY ET AL MANUFACTURE OF ARTIFICIAL FILAME Filed Fb. '27, 1957 United States Patent 2,900,221 MANUFACTURE OF ARTIFICIAL FILAIVIENTARY MATERIALS OF HIGH BULK John William Grebby, Selwyn George Hawtin, and John Downing, all of Spondon, near Derby, England, assignors to British Celanese Limited, a British company Claims priority,

This invention relates to the manufacture of artificial filamentary materials having a high bulk or voluminosity and good textile properties.

It is an object of the present invention to provide a method of making artificial filamentary materials which shall not only have a high tenacity and good extensibility, but shall also be of a voluminous nature, in the sense (in which the term is used throughout this specification) of having a low apparent density owing to the presence of internal cavities or voids, rather than as the result of the presence of loose loops of individual filaments, as in the so-called textured yarns, or of actual distortion of the fibre such as crimping. These properties are of considerable value for example in yarns to be used in carpets.

According to the invention an acetone solution of an acetone-soluble copolymer of vinylidene chloride and acrylonitrile, preferably containing 20-50% of acrylonitrile, is extruded in the form of filaments into an aqueous acetone coagulant, and the filaments formed are washed substantially free from acetone, stretched while in a softened condition at an elevated temperature, and then heated to a temperature below that at which they become softened without further stretching and preferably while allowing them to shrink by at least 50% of the amount by which they will shrink when completely free from restraint. It is usually advisable to dry the washed yarn before stretching it.

The copolymer from which the filaments are formed may advantageously be made by the emulsion polymerisation method, for example as described in British Patent No. 643,198 of British Celanese Limited. Its concentration in the spinning solution may be between about and 32%, the precise concentration preferably being chosen to give the solution viscosity most suitable for spinning under the other conditions prevailing. Generally solutions of concentration about 18-25% are very satisfactory when, as is most convenient, the solution is fed to the spinning jet at room temperature, say at about 18-25 C. The invention is of particular value in connection with copolymers containing 40-48% of acrylonitrile, and it will be described in more detail with special reference to such copolymers.

As the coagulant it is preferred to use an aqueous acetone of concentration about 920% and especially about 11-14% by weight at a temperature of about 40-60- C. Any suitable form of wet spinning apparatus may be used. For example the spinning solution may be extruded more or less horizontally into one end of a trough or the like containing the coagulant, and the filaments drawn from the coagulant at or near the other end. It is however preferable that the freshly formed filaments and the coagulant should be caused to travel together through a narrow tube; such a tube may with advantage be positioned vertically above and coaxially with an upwardly facing spinning jet contained in a wider extrusion chamber, so that the filaments and the coagulant travel up it together.

One example of a spinning 2 apparatus of this kind is described in US. application Ser. No. 323,788, filed December 3, 1952.

After leaving the coagulant the filaments, which will as a rule now be in the form of a bundle or yarn, are washed, preferably with water at a temperature up to about 50 C.- until they are substantially free from acetone, after which they are preferably dried. It has been found essential to remove the acetone by washing and not by, evaporation, since in the latter case the desired voluminous yarn is not obtained. Advantageously the yarn is washed continuously with its formation, for example while passing it round a pair of thread-storage thread-advancing rollers or a thread-storage thread-advancing reel (hereinafter referred to generally as advancing rollers). Subsequent drying should be carried out at a fairly low temperature, in particular a temperature below 50 C., for example 28-35 C., and may be done-either continuously, as by passing the yarn in a number of laps round heated advancing rollers over which also a current of warm air may be passed, or batchwise in the form of packages. It is in any case preferable to package the yarn, e.g. on bobbins, before stretching it, and it is convenient to use this opportunity to insert at least a low degree of twist, say 1-4 turns per inch.

The yarn is now stretched while softened to some extent in order to orientate it and increase its tenacity. While it is possible to stretch the yarn While it is softened by means of hot water or wet steam at a temperature of for example l20 C., a much more satisfactory product is obtained by stretching the yarn while it is softened by dry heat, preferably at about l70-215 C. For example the yarn may be drawn under a stretching tension through a slot in a metal block which is kept at a constant temperature, as by electric heating. Devices of this kind are already known in connection with the manufacture of yarns from synthetic high polymers such as nylon. The best results are usually obtained with the block at a temperature of -2l0 C., the length of the slot and the rate of travel of the yarn being such that the yarn will attain a temperature quite close or substantially equal to that of the block before it leaves the slot.

Thestretch ratio (i.e. the ratio of the length of the stretched yarn to that of the unstretched yarn) may be varied to some extent, but is preferably between about 3:1 'and 10:1, ratios between 5:1 and 7:1 being most advantageous. It is one of the disadvantages of using hot water to soften the yarn that the stretch ratio obtainable is nsually not more than about 3:1. Not only does a higher degree of stretch increase the tenacity of the yarn to a greater extent, but it also enables a yarn of finer denier to be made, or alternatively enables larger spinning orifices to be used in making a yarn of a given final denier. This has some advantage, for example in reducing both the pressure needed to force the spinning solution through the'or-ifices, and also the risk of individual ,orifices becoming blocked.

Yarn stretched to a ratiobetween about 5:1 and 7:1 may have a tenacity between about 3.5 and 4.5 grams perdenier and an extensibility of about 9-11%, while yarn stretched to a ratio of about 4:1 may have a tenacity of about 2-2.8 grams per denier and an extensibility of about l0-12%. While these tenacities are more than adequate for most purposes, it is desirable to increase the extensibility. This can be done by subjecting the yarn to afrelaxingi operation in which it is heated to a temperature belowitssoftening temperature but high enough to cause it to shrink by atleast 5% of its length. During thisoperation the yarnis allowed to shrink either quite freely. Or at any rate by at least 50 and advantageously at least 75%, of ,theamount by which it will about 100 125 shrink when free from all restraint. For example the yarn may be heated in bank or similar form under dry conditions to about 120-160 C., and especially about 125-145 C., forbetween about 5 minutes and 3 hours, although at temperatures above about 145 C. the duration of heating should generally be kept to a minimum in order to reduce or avoid possible discoloration of the yarn. Alternatively the relaxing treatrnent may be carried out continuously, as by passing the yarn through a heated zone under conditions allowing the desired degree of shrinkage to take place; thus it may be passed through a tube heated to the necessary temperature, which will usually be considerably higher than that which the yarn is actually to reach, which itself should not be much below the softening temperature. As an example, with yarn speeds between about 15 and 30 metres per minute a tube about a metre long may be heated to a tempera ture between about 180 and 250 C., the best temperature forany particular case being readily found by simple trial. Instead of dry heat, Water or wet steam at temperatures between about 90 and 130 C., especially C., may be used, in which case the time of treatment may be about /z2 minutes, though it can be longer if desired, e.g. up to 23 hours. Short treatment times are of course an advantage when it is desired to operate a continuous process.

The relaxing treatment not only causes a considerable increase in the extensibility of the yarn, which can indeed be more than doubled, but it also stabilises the yarn against subsequent shrinkage at elevated temperatures. For example a yarn when treated with boiling water before relaxation may shrink by some 14%, but after relaxation such shrinkage may be less than 1%.

If for any purpose a yarn of fairly low or moderate extensibility is required, e.g. an extensibility below about 13%, it may be rendered dimensionally stable by heating it under the same conditions except that it is held against shrinkage; for example it may be heated as a tightly wound package on arigid support. An intermediate degree of improvement in the extensibility is obtained when the yarn is held under tension such that a limited amount of shrinkage is allowed.

In addition to their other valuable properties the new materials have a very low degree of inflammability and a useful degree of resistance to attack by manychemicals, including acids.

Yarns obtained in accordance with'the invention may be employed as continuous filament yarns, or they may be cut into staple lengths which may be converted into spun yarns either alone or blended with other fibres, for example cotton, regenerated cellulose or cellulose acetate fibres. Both the continuous filament and the spun yarn, when of a suitable denier, form useful carpet yarns.

The invention is illustrated by the following example.

Example An acetone-soluble copolymer of vinylidene chloride and acrylonitrile comprising 42.6% by weight of acrylonitrile and having a specific viscosity of 0.93 was dissolved in acetone to give a solution of concentration 21.5%. The solution so obtained was filtered and then extruded through a spinning jet containing 26 orifices of diameter 0.130 mm. into aqueous acetone of concentration 12.6% by weight and at a temperature of 50% C. The filaments so formed and the aqueous acetone were passed together up a 6 ft. long spinning tube mounted vertically above the spinning jet. At the top of the tube the filaments came together to form a yarn, which Was drawn from the tube and thoroughly washed with cold water on advancing rollers until it was substantially free from acetone, after which'it was dried at a temperature of 35 C. and wound up and simultaneously given a twist of 2 turns per inch.

The dried yarn was then stretched to a ratio of 6:1 while passing through a slot in a metal block 18 inches long heated to a temperature of 200 C. The stretched yarn was formed into hanks and relaxed by heating for 1 hour to C. while quite free to shrink. During this treatment the denier of the yarn increased from 55 to 63. After the treatment the yarn had a tenacity of 3.12 grams per denier and an extensibility of 18.4%. If instead of being subjected to dry heat the stretched yarn was treated for 1 minute with wet steam at a temperature of 118 C., a product of denier 65, tenacity 2.90 grams per'denier and extensibility 21.3% was obtained. In both cases the yarn finally obtained could be boiled in water without shrinking by as much as 1%, and was markedly voluminous in character. The yarn was suitable for direct use, e.g. as a knitting yarn, or for combining with similar yarns to make a tow which could be cut into staple fibre for spinning into a useful carpet yarn.

An alternative method of relaxing the yarn, which gave a very similar product, consisted in feeding it at a speed of l9metres per minute into a tube 3 feet long heated to 200210'C., and taking it up at 17 metres per minute, thus allowing it to shrink by just over 10%.

By'employing spinning jets containing a large number of holes, a high "denier material suitable for use as a tow can be obtained at each spinning position.

When the copolymer contains less than 40% of acrylonitrile the temperatures used both for the stretching and "the relaxing operation may be rather lower.

Apparatus which may be used for the manufacture of voluminous yarns in accordance with the invention is illustrated diagrammatically in the accompanying drawing, in which Figure 1 is a side View, partly in section, of the spinning, washing and drying section of the apparatus, and

Figure 2 is a plan View of the stretching section of the apparatus, by means of which the stretched yarn is obtained in hank form ready for the relaxation step.

Referring now to the drawing, the apparatus illustrated in Figure 1 comprises a cylindrical extrusion chamber 3 provided with diametrically opposite inlets 4- for a coagulating liquid. A feed pipe 5 leads to a spinning jet 6 mounted axially within the chamber 3 and facing upwards. A spinning tube 7, also coaxial with the chamber 3, extends upwardly from it. A frusto-conical guide member 8 is fitted in the chamber 3, and serves to guide the flow of liquid smoothly from the chamber into the setting tube. A collector head 9, provided with a run=otf i0, surrounds the upper end of 'the spinning tube. A godet 11 is mounted above the upper end of the spinning tube and tangentially to its axis.

The apparatus comprises also a washing device 12, drier 13, and a take-up device represented by a bobbin 14. The washing device comprises a pair of rollers 15, 16 one above the other and having their axes skew with respect to each other to cause them to act as advancing rollers in the known way. Both rollers are mounted with their axes at an angle to the horizontal. Above the higher end of the lower roller 15 i a nozzle 17 fed by a feed .pipe 18 for washing liquid. A tray 19 provided with a run-off 20 is fixed below the lowerroller to receive liquid falling from it anywhere along its length. The drier 13 comprises a pair of heated advancing rollers 21.

In operation a coagulating liquid, usually aqueous acetone as already described, is fed continuously through the inlets 4 into the extrusion chamber 3, whence it passes up the spinning tube 7 into the collector head 9, which it leaves by the run-off 16, being then returned either to storage or to the extrusion chamber, if necessary after reheating it and/or adjusting its composition. At the same time a spinning solution is extruded into the coagulating liquid through the spinning jet 6, forming filaments 22 which come together at or near the top of the tube 7 to form a yarn or tow 23. The yarn or tow is drawn from the tube 7 bythe godet '11, and passed first to the washing device 12, Where-it is washed with water until it is substantially free from acetone, and then to the drier 13, and finally wound up.

Figure 2 illustrates a form of apparatus used for stretching yarn or tow which may have been made on the apparatus illustrated in ply, represented by a bobbin 24, an input stretching roller 25, a heatable metal block 26 having a longitudinal slot 27 for the passage of a yarn, an output stretching roller 28 which can be driven at a higher peripheral speed than the input roller 25, a roller 29 serving as a yarn guide, and a yarn take-up represented by a swift 30.

In operation the yarn or tow 23 is drawn from the supply 24 by the input stretching roller 25, from which it passes through the slot 27 to the output stretching roller 28, and round the yarn guide 29 to the take-up means 30. The block 26 is heated to a temperature high enough to soften the yarn or tow as it moves through the slot 27, and the relative peripheral speeds of the rollers 25 and 28 are adjusted to give the yarn or tow the desired degree of stretch.

Having described our invention, what we desire to secure by Letters Patent is:

1. In a process for the manufacture of artificial filamentary materials by forming filaments by spinning an acetone solution of an acetone-soluble copolymer of vinylidene chloride and acrylonitrile and stretching the filaments so produced while they are softened by heat and subsequently relaxing them by causing them to shrink by at least 5% of their length by the action of heat, the improvement which comprises in combination the steps of forming the filaments by extruding the copolymer solution into aqueous acetone, having a concentration of 9 to 20% by weight of acetone, as coagulant and as the next operations washing the filaments substantially free ttrom acetone with water and drying them.

2. In a process for the manufacture of artificial filamentary materials by forming filaments by spinning an acetone solution of an acetone-soluble copolymer of vinylidene chloride and acrylonitrile and stretching the filaments so produced while they are softened by heat and subsequently relaxing them by causing them to shrink by at least 5% of their length by the action of heat, the improvement which comprises in combination the steps of Figure 1. It comprises a yarn sup-,

forming the filaments by extruding the copolymer solu tion into aqueous acetone, having a concentration of 9 to 20% by weight of acetone, as coagulant and as the next operations Washing the filaments substantially free from acetone with water at a temperature of at most C. and drying them.

3. In a process for the manufacture of artificial filamentary materials by forming filaments by spinning an acetone solution of an acetone-soluble copolymer of vinylidene chloride and acrylonitrile and stretching the filaments so produced while they are softened by heat and subsequently relaxing them by causing them to shrink by at least 5% of their length by the action of heat, the improvement which comprises in combination the steps of forming the filaments by extruding the copolymer solution into aqueous acetone, having a concentration of 9 to 20% by weight of acetone, as coagulant and as the next operations washing the filaments substantially free from acetone with water at a temperature of at most 50 C. and drying them at a temperature of at most 50 C.

4. In a process for the manufacture of artificial filamentary materials by forming filaments by spinning an acetone solution of an acetone-soluble copolymer of vinylidene chloride and acrylonitrile and stretching the filaments so produced while they are softened by heat and subsequently relaxing them by causing them to shrink by at least 5% of their length by the action of heat, the improvement which comprises in combination the steps of forming the filaments by extruding the copolymer solution into aqueous acetone of concentration 11l4% by Weight at 4060 C. as coagulant and as the next operations washing the filaments substantially free from acetone with water at a temperature of at most 50 C. and drying them at a temperature of at most 50 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,517,570 Irons Aug. 8, 1950 2,679,450 Hampson et al. May 25, 1954 2,775,507 Downing et al Dec. 25, 1956 

1. IN A PROCESS FOR THE MANUFACUTRE OF ARTIFICIAL FILAMENTARY MATERIALS BY FORMING FILAMENTS BY SPINNING AN ACETONE SOLUTION OF AN ACETONE-SOLUBLE COPOLYMER OF VINYL IDENE CHLORIDE AND ACERYLONITRILE AND STRETCHING THE FILAMENTS DO PRODUCED WHILE THEY ARE SOFTENED BY HEAT AND SUBSEQUENTLY RELAXING THEM BY CAUSING THEM TO SHRINK BY AT LEAST 5% OF THEIR LENGTH BY THE ACTION OF HEAT THE IMPROVEMENT WHICH COMPRISES IN COMBINATION THE STEPS OF FORMING THE FILAMENTS BY EXTRUDING THE COPOLYMER SOLUTION INTO AQUEOUS ACETONE, HAVING A CONCENTRATION OF 